Doppler shift is maximal when the flow is parallel to the ultrasound beam.

Doppler shift is maximal when the flow is parallel to the ultrasound beam.

• A. True
• B. False
• C. Depends on angle
• D. Not applicable

Answer: (A)

Doppler shift depends on how much of the flow velocity is directed along the ultrasound beam. The frequency shift is proportional to the velocity component in the beam direction, which is v cos θ, with θ being the angle between flow and beam. When flow is parallel to the beam (θ = 0°), cos θ = 1, giving the largest possible shift. If the flow is opposite the beam (θ = 180°), cos θ = -1, and the shift has the same magnitude but opposite sign. As the angle moves away from alignment toward 90°, cos θ decreases toward zero, reducing the shift to zero at perpendicular flow. So the statement is correct, noting that the magnitude is maximal for flow along or directly opposite the beam, and practical Doppler sensitivity is best when the angle is as small as possible.

Doppler shift depends on how much of the flow velocity is directed along the ultrasound beam. The frequency shift is proportional to the velocity component in the beam direction, which is v cos θ, with θ being the angle between flow and beam. When flow is parallel to the beam (θ = 0°), cos θ = 1, giving the largest possible shift. If the flow is opposite the beam (θ = 180°), cos θ = -1, and the shift has the same magnitude but opposite sign. As the angle moves away from alignment toward 90°, cos θ decreases toward zero, reducing the shift to zero at perpendicular flow. So the statement is correct, noting that the magnitude is maximal for flow along or directly opposite the beam, and practical Doppler sensitivity is best when the angle is as small as possible.